Inside an Autonomous Agent: Discover via MCP, Coordinate via A2A, Transact via MPP
An autonomous agent completing a real task rarely uses one protocol — it typically discovers a tool through MCP, hands off part of the work to another agent through A2A. It pays for a service through MPP, all within a single request chain. Tracing that flow end-to-end shows how these three protocols function together as layers of one stack rather than competing standards.
Step 1: Tool Discovery via MCP
Before an agent can act, it needs to know what tools exist and what they do — this is MCP's job.
The handshake. Discovery doesn't start with a plain "list tools" call. The client sends a JSON-RPC 2.0 initialize request describing its own capabilities (like supportsToolDiscovery and maxToolCount), and the server responds with its own capability set. Only after this mutual negotiation does actual tool enumeration begin.
